A compound which undergoes decomposition upon exposure to light to produce a free radical (free radical generator) is well known in the field of the graphic arts, photosensitive recording materials, etc. It has wide application as a radical photopolymerization initiator incorporated in a photopolymerizable composition, a light activator incorporated in a free radical-containing photographic composition, a photo-initiator for a reaction catalyzed by an acid generated upon exposure to light, or the like. Such a free radical generator has been used to prepare a variety of photosensitive materials useful in printing, duplicating, copying and other recording material systems.
Bis(trihalomethyl)-s-triazine compounds have been proposed as free halogen radical generators which are sensitive to light of a wavelength ranging from the near ultraviolet region to the visible light range. These compounds are further described in U.S. Pat. Nos. 3,954,475, 3,987,037, 4,189,323, 4,696,888, 4,837,128, JP-A-62-58241 JP-A-2-149570 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), etc. Though sensitive to light of a wavelength ranging from the near ultraviolet region to the visible light range, these compounds are disadvantageous in that the products of decomposition by exposure are liable to have light yellow coloration. These compounds are also disadvantageous in that when used in a system where a radical photopolymerization initiator or its decomposition products remain in the recording layer, the recording layer becomes yellow in color due to the decomposition of the residual compounds by exposure to light during storage in bright places. The inventors made extensive studies to overcome these problems. As a result, it has been found that the compound according to the present invention exhibits excellent properties.
In connection with the compound according to the present invention, JP-A-58-40302 discloses a compound represented by formula (IV): ##STR4## wherein R.sup.9, R.sup.10 and R.sup.11 each represent an alkyl, aryl, alkenyl or piperidino group which may have substituents, --NR.sub.2, --OR or --SR, in which R represents a hydrogen atom or an alkyl group, with the proviso that at least one of R.sup.9, R.sup.10 and R.sup.11 represents a monohalogen-, dihalogen- or trihalogen-substituted methyl group.
In specific examples of the compound and the examples, however, only monohalogen-, dihalogen- or trihalogen-substituted methyl groups having two or three halogen substituents on one triazine ring are disclosed. Only chlorine atoms and bromine atoms are disclosed as halogen substituents. No examples of the compound having a fluorine atom substituent are disclosed. Of course, there is no reference to the interesting properties of a photosensitive s-triazine compound having one trichloromethyl group or tribromomethyl group according to the present invention.